Further observations on the fine structure of the infracerebral gland in Nereis (Annelida; Polychaeta) — C₂ and C₃ cells; centripetal and centrifugal fibers

Abstract

The infracerebral gland of Nereis is made up of three types of cells. C, cells are hypertrophied pericapsular elements, whereas C, and C, cells have the morphological and cytological features of neurosecretory neurons. C, and C, cells give rise to centripetal "proximal processes" which extend into the brain through the midventral pocket formed by delamination of the brain capsule. Their "distal processes" terminate within the gland or its immediate vicinity. "Centrifugal fibers" arise from nerve cells located within the brain and appear to synapse upon the proximal processes of c, cells in the region of the midventral pocket and in the ventral region of the brain. The cytology of C, and C, cells suggests that they are the source of distinct peptide hormones.